Add Agent-assisted feedback preview

[mattheliu]

What changed

• rename the single composer entry to 让 Agent 帮我反馈
• make the Agent role explicit: format Host health plus user-selected closed enums, without reading conversation content
• show a dedicated send-before-preview card and require a separate 确认发送这条反馈 click
• remove message identifiers from the active feedback controller and RPC call path
• keep the submitted Session history card model-invisible and durable
• bump the public package to 0.4.3

Why

The feedback action should feel Agent-assisted without using the current task or local conversation as analysis input. The user must be able to inspect the complete human-readable feedback before any network request occurs.

Verification

• pnpm test:all
• 26 client/unit tests passed
• 10 backend tests passed
• server build passed
• real DSH 0.1.0-rc.6 plugin E2E passed
• local browser verification: preview added one local draft and zero share requests; confirmation added one share request, one receipt, and one Session card